<?php
$a =$_POST["username1"];
$b = $_POST["username2"];
$c = $_POST["num1"];
$nba = true;
if(is_numeric($a)==$nba){
	intval($a);
}else{
	exit("请输入正确数字！！");
}
if(is_numeric($b)==$nba){
	intval($b);
}else{
	exit("请输入正确数字！！");
}
if($c=="+"){
	$s =$a+$b;
}
if($c=="-"){
	$s =$a-$b;
}
if($c=="*"){
	$s =$a*$b;
}
if($c=="/"){
	$s =$a/$b;
}
echo $a.$c.$b."=".$s;